1. Field of the Invention
The present invention relates to a vibration wave driving device (typically, a vibration wave motor). In particular, the present invention relates to a vibration wave motor which is characterized by its supporting structure.
The present invention relates also to a structure of a vibration wave driving device, in particular to a structure which does not cause creak or a like noise.
2. Related Background Art
Various types of vibration wave driving devices, typically ultrasonic motors (vibration wave motors) are known, including rotary types and linear types.
The vibration wave driving device comprises, as basic structural elements, an elastic member constituting a vibrator, an electromechanical conversion device (or a magneto-stricting element), a supporter for supporting the vibrator, a driven member driven frictionally by contact with a part of the vibrator, a pressure-applying unit, and a bearing guide.
FIGS. 8A and 8B illustrate a constitution of a conventional linear type vibration wave motor (U.S. Pat. No. 7,432,633). FIG. 8A is a front view and FIG. 8B is a side view thereof.
Piezo-electric element 15 in a horizontally long rectangular shape is held by holder 19, energized by blade spring 20 toward driven member 17, and brought into contact with driven member 17 by driving contacts 16.
Holder 19 has side walls 22 for holding piezo-electric element 15 in the Y-direction, holder base 23, and pin 18 in a cylindrical shape projecting in the Y-direction from side wall 22.
Pin 18, which is nearly circular cylindrical, supports piezoelectric element 15 to be rotatable around pin 18 to follow smoothly the movement of driven member 17.
On application of an alternate electric field to piezoelectric element 15 by a power source and a power applying means not shown in the drawing, the vibrator containing piezo-electric element 15 is excited in a bending oscillation mode in the X-Z plane, and in a stretching mode in the X-direction simultaneously to move drive contacts 16 in an ellipsoidal movement. As the result, driven member 17 in contact with driving contact 16 is driven by blade spring 20 frictionally in the X-direction.
In the above conventional vibration wave motor, although the linear bearing guide is not shown in the drawing, with the parts upper from piezo-electric element 15 (members 15-23) fixed, the driven member 17 is guided to move only in the X-direction (in the direction of the driving force).
Such a driving system employing a linear type vibration wave motor is advantageous in that the construction is simple in comparison with the conventional driving system which converts the rotational movement of an electromagnetic motor into linear movement, and that the positioning accuracy can be improved by direct driving.
U.S. Pat. No. 7,425,770 discloses a linear type of vibration wave motor employing a magnetic force for pressure application.
Various types of ultrasonic motors are known, including rotary type ones and linear type ones.
The ultrasonic motors are classified roughly by the driving principle into stationary wave type ones and progressive wave type ones. The stationary wave type vibrator forms a stationary wave as a driving vibration mode by superposition of a bending vibration and a stretching vibration excited simultaneously. On the other hand, the progressive type vibrator forms similarly a progressive wave by superposition of a plurality of stationary wave vibrations.
Japanese Patent Application Laid-Open No. 2006-271143 discloses a progressive wave type of ultrasonic motor having the structure illustrated in FIG. 22.
In FIG. 22, the ultrasonic motor comprises vibrator 101 having piezo-electric member 102 and an elastic member 103, and moving member 105 in pressure contact with the driving face of elastic member 103. Flange 103c at the inner periphery of vibrator 101 is held and fixed between supporting members 106a, 106b to enable driving of moving member 105.
Moving member 105 is joined to shaft 108 with interposition of buffering member 107 like a rubber, and pressure spring 109 and output gear 110 fixed to shaft 108 apply a pressure to the frictional face between moving member 105 and vibrator 101.
The ultrasonic motor having such a structure is capable of outputting a larger torque at a lower speed with generation of less noise.
Japanese Patent Application Laid-Open No. 2001-268949 discloses an ultrasonic motor which has disk-shaped vibrator 113 supported at the center by support member 114 as illustrated in FIG. 23.
In this ultrasonic motor, the vibrator 113 is comprised of a combination of elastic member 111 and piezo-electric element 112, and vibrates in a vibration mode of primary vibration in the radial direction, in which the center of the disk becomes the center of the vibration and the outermost periphery of the disk becomes the loop. Therefore in this constitution, the node of the vibration, namely the center of the disk, is fixed not to prevent the vibration of the vibrator.    (Patent Document 1) JP-A 2006-211839; U.S. Pat. No. 7,432,633    (Patent Document 2) JP-A 2006-340443; U.S. Pat. No. 7,425,770    (Patent Document 3) JP-A 2006-271143    (Patent Document 4) JP-A 2001-268949
In the aforementioned U.S. Pat. No. 7,432,633, the support portion is comprised of pin 18, holding member 19 engaging with the pin to control the position and direction of the vibrator, and blade spring 20. The vibrator is pressed against driven member 17, whereby the position and the direction of the vibrator are controlled. This results in a larger thickness of the device, and is not suitable for miniaturization of the entire motor.
This structure contains no damping member within the combination of the vibrator, holding member, and blade spring. Therefore, a slight leakage of vibration of the vibrator or an undesired vibration transmitted from the friction part during the driving tends to cause an abnormal noise like a creak disadvantageously.
The above-mentioned conventional ultrasonic motors have problems as below.
In the ultrasonic motor described in Japanese Patent Application Laid-Open No. 2006-271143, the vibration member is made of a less-damping material owing to the characteristic driving principle of utilizing the vibration and friction. Further, the friction material is selected which has a high frictional coefficient, which tends to cause undesired vibration and noises.
Such phenomena become remarkable in cost down of the vibrator or the moving member owing to lowering of the face precision of the sliding face.
This prevents simultaneous achievement of improvement of the function such as the low noise and the low cost.
To overcome the above disadvantages, a damping rubber is attached on the back face of the vibrator (on the joint face to a flexible substrate). However, the damping rubber damps simultaneously the driving vibration of the vibrator to lower the motor efficiency disadvantageously.
Further, the ultrasonic motor disclosed in the above Japanese Patent Application Laid-Open No. 2001-268949 has also shortcomings of occurrence of creak or a like noise by stick slippage at a sliding portion, or a like cause.
To solve the above problems, the present invention intends to provide a vibration wave driving device having a simplified and thinned supporting structure to miniaturize the device and to lower the production cost.
The present invention intends also a vibration wave driving device which damps effectively undesired vibration excited in the sliding face without damping the driving vibration of the vibrator and prevents occurrence of creak or a like noise.